The present invention relates to an optical device module, for example, for use of optical communication, and particularly to the fixing structure of the optical fiber, which is inserted into a package of the module.
Optical device modules including semiconductor laser devices, Photo-diode devices and optical receiving devices, have widely been used in optical communication systems. A structure of fixing the optical fiber in a package of the optical device module has been known in prior art. Such a structure is disclosed in FIGS. 5 and 6 in U.S. Pat. No. 5,619,609.
FIG. 5 is a cross sectional view of a main part of an optical device module including a package 2 made of metal or ceramic material, an optical device 1, such as a semiconductor laser device, mounted on a stem 8 inside the package 2, and an optical fiber 4 which is arranged in the package and passes through an insertion tube 3 fixed through the wall 21 of the package 2
A ferrule 5 is fixed on the stem 8 to holding an end portion of the optical fiber and the optical fiber extends form the ferrule 5 to an outer side of the package 2 through a through-hole 6 of the insertion tube 3. The ferrule 5 is adjusted to align the optical axis of the optical fiber 4 to the optical axis of the optical device 1, so that the ferrule 5 is fixed via a ferrule holder 7 to the stem 8.
In general, in the module where a semiconductor laser must be aligned precisely to the optical fiber on a single optical axis, when the optical fiber 4 is fixed by soldering directly to any fiber holder, the axis of the optical fiber often displaces over 10 xcexcm from the original optical coupling point of the laser emission device. As a result, the laser output from into optical fiber largely is reduced. The soldering structure of the fiber makes it difficult to readjust correct optical fiber position, therefore, avoiding ferrules from directly being soldered. Also adhesives can not be employed in the package 5, because adhesives generate organic gas has a fear of lowering the life time of semiconductor laser devices. Thus, the optical fiber 4 is laser welded and fixed through the ferrule 5.
The stem 8 is usually installed on a thermoelectric cooling element 9 for controlling the temperature of the optical device 1.
The insertion tube 3 and the optical fiber 4 are metalized by gold plating, etc, and the solder is poured into a soldering gap 10 of the insertion tube 3 so that the package is air-tightly sealed. The optical fiber 4 is fixed between the ferrule 5 and the airtight sealing portion of the insertion tube 3 in such a manner that the optical fiber is linear and substantially parallel with respect to the optical axis.
In FIG. 6 showing the ferrule fixing structure in FIG. 5, the ferrule 5 and the ferrule holder 7 are positioned to optically align the optical fiber 4 to the optical axis of the optical device, and then the ferrule holder 7 is fixed onto the stem 8 with the ferrule 5 fixed on the ferrule holder 7, by laser welding. The conventional ferrule holder 7 has a U-shaped groove portion 12 and flange portion 11 on both sides of the groove machined by a milling cutter from a metal block. As shown in FIG. 6, the flange portion 11 is directly laser-welded onto an upper surface of the stem 8 and the ferrule 5 is fillet welded onto both edges of the U-shaped groove portion 12.
FIG. 7 shows a cross-sectional view of a prior art optical device module having an optical fiber disposed in a bending manner in a package. The optical fiber 4 is supported at its end portion by a first ferrule 5 on a stem 8, and held on a rear side thereof by a second ferrule 13 which is disposed within an insertion tube 3 through a wall of the package 2.
The first ferrule 5 is fixed on a ferrule holder 7 which is fixed on a stem 8 by laser welding. Then the second ferrule 13 is inserted through an insertion tube 3 from the outside thereof and is pushed into tho inside of the package 2. To seal the package air-tightly, the optical fiber 4 is soldered to the second ferrule 13.
In this packaged optical fiber, the optical fiber is bent in the form of arc between the first ferrule 5 and the second ferrule 13. Such a second ferrule 13 is necessary as a member fixing the end of the fiber for bending the optical fiber 4 in the package 2.
The conventional optical device module, as shown in FIGS. 5 and 6, has drawbacks due to the structure of the optical fiber 4 in the package 2 fixed so as to be linear and substantially parallel to the optical axis. Therefore, changes in environmental temperature cause the package 2 to expand or contract, and male the optical fiber 4 in the package 2 suffer from a tensile or compressive stress, causing the swinging of the end surface of the optical fiber 4 to be coupled to the optical device.
An first problem is that the output transmitting from the optical emission device to the optical fiber fluctuates and that the optical fiber tends to deteriorate the optical performance by vibration. A second problem is that separation of the soldering material from the optical fiber in the insertion tube 3 is caused by the repeated tensile and compressive stress between the ferrule holder 7 and insertion tube 3, leading to insufficient airtight sealing. No easy or secure airtight sealing can be achieved, particularly, by the enlarged length between the insertion tube 3 and the optical fiber 4.
Although the optical device module in prior art, as shown in FIG. 7, can solve the first problem by bending the optical fiber 4 in the packager 2, the optical device module requires a second ferrule 13 as a fixing member, or grip for bending the optical fiber 4. In addition, airtight sealing between the optical fiber 4 and second ferrule 13 is required, as well as sealing between second ferrule 13 and the insertion tube 3 of the package. Such double airtight sealing structure may deteriorates production efficiency with low production yield. As a result, this structure of optical device modules can not solve the above second problem.
An object of the present invention is to provide an optical device module in which an optical fiber can derive optical output stablly from an optical device packaged in the module, even in use under the circumstances of the package extending or contracting due to environmental temperature changes.
Another object is to provide an optical device module having an easy and secure airtight sealing structure which can decrease in the number of the fabricating steps, and increase in productivity of the modules.
According to the present invention, an axis of an optical fiber at the end portion whose end surface is coupled to an optical device is offset with respect to an axis of the optical fiber at a fixing portion where the fiber is fixed through a wall of a package which contains the optical device and the part of the fiber so as to bend the optical fiber in a region of between the end portion of the fiber and the fixing portion within the package.
The offset between of the axis of the optical fiber at the end portion and the axis thereof at the fixing portion allows the optical fiber to naturally bend, and then the bent fiber can absorb the expansion and contraction of the package length due to the temperature change of the environment, resulting in preventing effectively fluctuation output of the optical fiber and deterioration of the optical fiber.
In the present invention, preferably, a ring member having an fiber inserting hole can be inserted co-axially into an insertion tube fixed through the wall to hold the optical fiber, and then the fiber, ring member and insertion tube can be sealed to each other to obtain good airtight seal.
In the present invention, a ferrule for holding the end portion of the optical fiber may be fixed to a ferrule holder capable of being deformed plastically in the package. After fixing the optical fiber, the plastic deformation of the ferrule holder enables the optical axis of the optical fiber to optically align to an emission end of the optical device.
The optical device in the optical device module according to the invention includes a semiconductor optical emission or reception device, such as a semiconductor laser emission device, photo-diode device.